This invention relates to novel polyether polycarbonate block copolymers and to polyurethanes derived from the block copolymers.
Polyether polyols are well-known polymers which can be further polymerized with organic polyisocyanates to prepare polyurethanes. Polyether polyols are prepared by the reaction of hydroxy-containing hydrocarbons, such as an aromatic or aliphatic diol and epoxides, for instance ethylene oxide and propylene oxide.
It is known to prepare polycarbonates from aliphatic dihydroxyl compounds either by a process of phosgenation in which hydrogen chloride is liberated or bound by bases, such as pyridine or quinoline, or by a process of transesterification with carbonic acid esters of alcohols or phenols, preferably diphenylcarbonate, optionally with the aid of transesterification catalysts.
In either case, it is essential to use phosgene or a mixture of carbon monoxide and chlorine as source of carbonic acid. Technical processes which involve the preparation and handling of phosgene are difficult and costly on account of the considerable safety risks involved and the high cost of materials due to corrosion. To this are added ecological problems since either the spent air is contaminated with hydrogen chloride or the effluent water with sodium chloride.
Polycarbonates produced by these methods may have a functionality of less than two due to inadequate or incomplete esterification or transesterification which often prevents the products from forming high molecular weight polymers in subsequent reactions.
One method for preparing polycarbonates is illustrated by Malkemus, U.S. Pat. No. 3,133,113. It is disclosed that an alkylene carbonate such as ethylene carbonate can be reacted with a glycol such as diethylene glycol in a mole ratio in the range of 1.2:1 to 2.5:1 at reduced pressure while removing ethylene glycol formed by the reaction until the reaction in complete. The catalyst employed is a mixed zinc borate-alkaline earth metal oxide catalyst.
Stevens, in U.S. Pat. No. 3,248,414; 3,248,415 and 3,248,416, discloses the preparation of polycarbonates from: (1) carbon dioxide and 1,2-epoxides; (2) cyclic carbonates such as ethylene carbonate; or (3) from cyclic carbonates and a 1,2-epoxide. A minor amount of a polyol is employed as an initiator. The reaction is usually conducted under pressure in the presence of a metal carbonate, metal hydroxide, trisodium phosphate or a tertiary amine.
Polycarbonates have also been prepared by polymerization of ethylene carbonates under pressure using basic catalysts and a minor amount of glycol as initiator. These products are low in carbonate and high in ether groups concentration due to decomposition of the ethylene carbonate.
In the processes described above, the products are polymers of relatively low molecular weight with a broad molecular weight range. Also, certain polyols which are often used as initiators, for example sucrose, undergo oxidation when exposed to the polymerization conditions used in the preparation of polycarbonates. The presence of these oxidized products often results in color in the resin prepared. The presence of color in such polycarbonates is undesirable for many uses.
What is needed is a polycarbonate which is multifunctional which also has a high molecular weight and relatively narrow molecular weight distribution. What is further needed is a polycarbonate which does not contain color-causing by-products. Polycarbonates which have good flame retardancy, thermal stability and load bearing properties are desirable. Further desirable are polycarbonates with relatively high carbonate content.